The invention is in the field of electronic reproduction technology and is directed to a method and to an apparatus for processing color values in view of a modification of the reproduction scale and/or of a correction of color offsets, the color values being generated by point-by-point and line-by-line, optoelectronic scanning of color originals.
For example, a point-by-point and line-by-line scanning of a color original is implemented in a flat bed color image scanner. Given such a flat bed color image scanner, the color original to be scanned is arranged on a planar originals carrier that moves continuously relative to an optoelectronic transducer of a scanner unit. The color original to be scanned is illuminated line-by-line with red, green and blue light in alternating fashion, and the scan light that is reflected by the color original or passes through the color original and is modulated with the color information of the scanned lines is converted into analog color values in the scanner unit.
The scanner unit is essentially composed of a source of scan light, of a rotating filter wheel for the line-by-line separation of the white light generated by the source of scan light into red, green and blue light, and of an optoelectronic transducer, for example of a photodiode line (CCD line) having a following signal editing unit for converting the color components "red", "green" and "blue" acquired point-by-point and line-by-line in the color original into the color values (R, G, B). The filter wheel comprises three color-selective segments that have different spectral transmission characteristics for "red", "green" and "blue". The scanner unit is followed by a color value processing unit wherein the analog color values (R, G, B) are, for example, digitized, processed for the following processes and then stored or output on-line.
A variation of the reproduction scale in comparison to the scanned color original is often undertaken in the reproduction of color originals, for which purpose a multitude of time-consuming calculation operations on the basis of the color values are required in the color value processing.
Given employment of a filter wheel in the optoelectronic scanner unit, the color components "red", "green" and "blue" of the color original are sampled successively line-by-line due to the continuous relative motion between the optoelectronic transducer and the color original. For example, only the color component "red" is first acquired in a scan line, only the color component "green" thereafter in the following scan line, and only the color component "blue" thereafter in the following scan line, i.e. at different locations of the original.
Disturbing color offsets arise due to this sequential color scanning in the individual scan lines of the color originals, since respectively only one color value of the color value triad is acquired for the individual picture elements of a current scan line.
It is already known for improving the reproduction quality to implement a color offset correction in that the lacking color values of the color value triads of a scan line are respectively calculated from the acquired color values of the neighboring scan lines.
Due to the considerable number of color values that are to be processed given a variation of the reproduction state, there is the problem that a color offset correction could hitherto not be implemented in a satisfactory way without considerably exceeding the time available for the calculation of the scale and thus disadvantageously reducing the speed in the color value processing. In the reproduction, an image sharpness correction or, respectively, contrast correction, is also often undertaken on the basis of an electronic unsharp masking wherein further time-consuming calculating operations with the color values must be undertaken.